DSPC vesicles

Because the dynamics of phospholipid membranes have been well characterized using AF probes [8-13], fluorescence results obtained with hydrated human SC were compared to aqueous suspensions of unilamellar distearoyl-phosphatidylcholine (DSPC) vesicles. DSPC was also used because its phase transition temperature (55°C) is close to that of SC lipids (65 C). The microenvironment inside DSPC and SC membranes was studied by measuring fluorescence lifetimes, and shifts in emission maxima were compared to excitation maxima (Stokes shifts), along with quenching of a series of AF probes by iodide. Stokes shifts (Av) [6] were calculated as ... 

Table 1 Steady-State Emission Maxima (kg ) and Calculated Stokes Shift (Av) for various n-AF Probes in Hexane, DSPC Vesicles, and Human SC at 20°C...

Table 2 Lifetimes (Ti, T2, Xavg)> Their Fractional Contributions Constants K v) of n-AF Probes in DSPC vesicles and human SC...

Remote Loading of Doxorubicin into DSPC Cholesterol (55 45) Large Unilamellar Vesicle... 

DSPC/Chol (55 45) LUVs (diameter = 100 nm) are prepared as described in section Preparation of Sphingomyelin/Cholesterol (55 45) Large Unilamellar Vesicle by Extrusion [(Lipid) = 20 mM, volume = 5mL], using 350 mM citrate pH 4.0 as the hydration buffer, and 20 mM HEPES 1.50 mM NaCl pH 7.5 (HEPES-buffered saline) as the external buffer. In this case, the pH gradient is formed during the final dialysis step. It would also be possible to omit the final dialysis step and form the pH gradient by one of two common column methods. This could be desirable if the LUV... 

The initial mixture and each time point are then assayed for ciprofloxacin and lipid. Lipid can be quantified using the phosphate assay (64,65) or by liquid scintillation counting. Ciprofloxacin is quantified by an absorbance assay following removal of drug from lipid by a Bligh-Dyer extraction procedure (78) (see below). The percent uptake is determined as described in the section Remote Loading of Doxorubicin into DSPC/Cholesterol (55 45) Large Unilamellar Vesicle. ... 

The preformed vesicle (PFV) approach involves incubation of liposomes containing a cationic lipid and a PEG coating with polynucleotides in the presence of ethanol. Typically, LUV composed of distearoyl-phosphatidyl-choline (DSPC), cholesterol (Choi), l-0-(2 -(oi-methoxy-polyethylene-glycol)... 

A similar study by O Brien and coworkers utilized bilayers composed of a shorter chain diacetylenicPC (9) and DSPC or DOPC [37]. Phase separation was demonstrated in bilayers by calorimetry and photopolymerization behavior. DSC of the 9/DSPC (1 1) bilayers exhibited transitions at 40 °C and 55 °C, which were attributed to domains of the individual lipids. Polymerization at 20 °C proceeded at similar rates in the mixed bilayers and pure 9 bilayers. A dramatic hysteresis effect was observed for this system, if the bilayers were first incubated at T > 55 °C then cooled back to 20 °C, the DSC peak for the diacetylenicPC at 40 °C disappeared and the bilayers could no longer be photopolymerized. The phase transition and polymerizability of the vesicles could be restored simply by cooling to ca. 10 °C. A similar hysteretic behavior was also observed for pure diacetylenicPC bilayers. Mixtures of 9 and DOPC exhibited phase transitions for both lipids (T = — 18 °C and 39 °C) plus a small peak at intermediate temperatures. Photopolymerization at 20 °C initially proceeded at a similar rate as observed for pure 9 but slowed after 10% conversion. These results were attributed to the presence of mixed lipid domains... 

In mixed bilayer vesicles diacetylenic and natural lipids exhibit the same miscibility behavior as in monomolecular films. This can be demonstrated using differential scanning calorimetry (DSC). The neutral lipid (23) is immiscible with DSPC or DOPC as indicated by the two phase transitions of the mixed liposomes which occur at the same temperatures as those of the pure components (Fig. 33 a). 

After vesicle polymerization the phase transition of the diacetylenic lipid has almost completely disappeared, while the phase transition of DSPC is unaffected by polymerization (Fig. 33b). The same holds true for mixtures of (23) with DOPC 62. ... 

CH, cholesterol DLPC, dilaurylphosphatidylcholine DMPC, dimyristoyl-phosphatidylcholine DMPG, dimyristoylphosphatidylglycerol DPPC, dipal-mitoylphosphatidylcholine DPPG, dipalmitoylphosphatidylglycerol, DSPC, distearoylphosphatidylcholine DSPG, distearoylphosphatidylglycerol MLV, multilameller vesicle PA, phosphatidic acid PC, phosphatidylcholine TA, triamcinolone acetonide. 

Evans et al. also showed that the 1 1 mixture of BAN and (3, y-distearoyl-phos-photidylcholine (DSPC) gives a smectic A texture in the temperature range of 57.3 to 100°C [21]. This is the first notice of lyotropic lamellar liquid crystals formed in the ionic medium. Additionally, Seddon et al. [28] and Neve et al. [29] have described the long-chained A-alkylpyridinium or l-methyl-3-alkylimidazolium ions to display smectic liquid-crystalline phases above their melting points, when Cl or tetrachloro-metal anions like CoCl " and CuCl " are used as the counter ions. Lin et al. have also noted the liquid crystal behavior of 1-alkylimidazolium salts and the effect on the stereoselectivity of Diels-Alder reactions [30]. However, liquid crystals are classified as ionic liquid crystals (ILCs), and they are distinguished from liquid crystals that are dispersed in ionic liquids. Although the formation of micelles and liquid crystal phases in ionic liquids have been thus reported, there has been no mention of the self-assembly of developed nano-assemblies that are stably dispersed in ionic liquids. In the next section the formation of bilayer membranes and vesicles in ionic liquids is discussed. 

Figure 4 Some phase diagrams for lipid bilayers in excess water prepared from binary and ternary lipid mixtures, a) Multibilayer lipid vesicles prepared from binary mixtures of DMPC and DPPC (24) b) Multibilayer lipid vesicles prepared from binary mixtures of DMPC and DSPC [adapted by Reference (25) from data for perdeuterated lipids published by Knoll et al. (26)] c) Multibilayer lipid vesicles prepared from binary mixtures of diCi/.QPC and C22 oCi2 oPC (27) d) Multibilayer lipid vesicles prepared from binary mixtures of DMPC and cholesterol (28) e) Multibilayer lipid vesicles prepared from ternary mixtures of palmitoyl sphingomyelin, POPC, and cholesterol [adapted by Reference (29), from data published by De Almeida et al. (30)] Lipid bilayers prepared from ternary mixtures of DSPC, DOPC, and cholesterol (31).

The formation of liposomes [or better arsonoliposomes (ARSL)], composed solely of arsonolipids (Ars with R=lauric acid (C12) myristic acid (C14) palmitic acid (C16) and stearic acid (C18) (Fig. 1) have been used for ARSL construction), mixed or not with cholesterol (Choi) (plain ARSL), or composed of mixtures of Ars and phospholipids (as phosphatidylcholine [PC] or l,2-distearoyl- -glyceroyl-PC [DSPC]) and containing or not Choi (mixed ARSL), was not an easy task. Several liposome preparation techniques (thin-film hydration, sonication, reversed phase evaporation, etc.) were initially tested, but were not successful to form vesicles. Thereby a modification of the so called one step or bubble technique (8), in which the lipids (in powder form) are mixed at high temperature with the aqueous medium, for an extended period of time, was developed. This technique was successfiil for the preparation of arsonoliposomes (plain and mixed) (9). If followed by probe sonication, smaller vesicles (compared to those formed without any sonication [non-sonicated]) could be formed [sonicated ARSL] (9). Additionally, sonicated PEGylated ARSL (ARSL that contain polyethyleneglycol [PEG]-conjugated phospholipids in their lipid bilayers) were prepared by the same modified one-step technique followed by sonication (10). 

PLGA (D,L)-poly(lactic glycolic acid), PEG poly(ethylene glycol), DSPC distearoyl-L-a-phosphatidylcholine, DSPG distearoyl-L-a-phosphatidylglycerol) Aerodynamic diameter, Liposome vesicle size... 

P. Hoyrup, O.G. Mouritsen, and K. Jorgensen. Phospholipase A2 activity towards vesicles of DPPC and mixtures of DMPC and DSPC with small amounts of SMPC. Biochim. Biophys. Acta, 2001,... 

The first set of experiments involved fluorescence resonance energy transfer (FRET) between the naphthalene and pyrene-laheled polymers. A 5 1 mixture of PNIPAM-Py to PNIPAM-Na was used. When assembled in micelles, the pyrene acts as a quencher to the naphthalene, leading to high pyrene fluorescence and low naphthalene fluorescence. When the mixture is added to DMPC (liquid phase) or DSPC (gel phase) vesicles at room temperature, naphthalene fluorescence is increased, while pyrene fluorescence is dramatically decreased. This effect is not seen with the PNIPAM-Py-Na polymer, so the reduction in FRET is not due to the hydrophobic environment. This means that the hydrophobic anchors of the PNIPAM-Py and the PNIPAM-Na likely enter the membrane and the dyes are moved apart from one another. The fact that the anchor appeared to insert into the gel-phase DSPC membrane was somewhat surprising. The authors attribute the effect to defects between crystalline domains in the membrane. To test if the LCST transition still occurs when the polymers are anchored to the membrane, differential scanning calorimetry (DFC) was used. The LCST transition of the PNIPAM-Py/PNIPAM-Na mixture in solution was observed in the DFC ttace. When combined with DSPC or DMPC vesicles, the same peak was observed, indicating that the transition does indeed stiU occur, even in the presence of the lipid. 

Both DPPC and DSPC have transition temperatures well above ambient which means that these vesicles were held together tightly by the bilayers in their gel state. 

The spectroscopic and thermodynamic data presented above suggest a correlation between molecular order, interfacial packing and the gel to liquid crystalline phase transition temperature. Aqueous phospholipid vesicles above their transition temperature readily form tightly packed, well-ordered monolayers at a water/CCU interface (e.g. DLPC). Vesicles below their transition temperature possess greater stability, forming monolayers which are considerably expanded and which show greater disorder (i.e. DPPC and DSPC). 

After forming a tightly packed DSPC monolayer above T, reducing the temperature below does not lead to a corresponding reduction in the interfacial pressure that would accompany removal of DSPC molecules from the interface. The irreversible nature of monolayer formation is not surprising. With an enthalpy of solvation in CCI4 of 4.5 kJ/mol per CH2 unit [59], alkyl chains once adsorbed to the water/CC interface face a very steep barrier to desorption and vesicle re-formation. The irreversible nature of the adsorption process can be used to... 

In marked contrast to the behavior seen in the previous two examples, spherical vesicles made of saturated lipids l,2-distearoyl-s -glycero-3-phospho-choline DSPC, T = 54.9°C), show only a liquid to gel phase transition at 47.8°C when... 

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